The engine control module (ECM) regulates the ignition coils and checks their function via a separate diagnostic cable. The diagnostic trouble code is generated if the control module detects that the signal for an ignition coil is faulty.

Fault symptoms may include:

Malfunction indicator lamp (MIL) lit

The engine is not firing on all cylinders

The diagnostic trouble code can be diagnosed when the engine is running and will indicate which ignition coil is involved.